Catalytic method of preparing unsaturated acids and aldehydes



States nit This invention relates to new and useful catalysts and to a method of preparing unsaturated aldehydes and unsautrated carboxylic acids by oxidation of unsaturated hydrocarbons at an elevated temperature, and relates more particularly to catalysts comprising a mixture of a molybdenum oxide, tellurium oxide and a metal phosphate of a metal of the fourth period of Group VIII of the Periodic Table in a molar ratio of 100 M -100 TeO and 10-100 of the metal phosphate and to a method of preparing acrolein and acrylic acid or methacrolein and methacrylic acid by passing vapors of propylene or isobutylene and an oxygen containing gas over the catalyst at a temperature of from about 325 C. to about 550 C. The catalyst can also be designated as wherein M is a metal of the fourth period of Group VIII, iron, nickel and cobalt, with the P being in the form of a phosphate i.e., each P is attached to 3 or 4 oxygen atoms.

Numerous attempts have been made in the past to prepare products of higher oxidation state from hydrocarbons, especially from the normally gaseous hydrocarbons. However, all prior catalysts and procedures for oxidizing monoolefinic gaseous hydrocarbons to monoolefinically unsaturated aldehydes or monoolefinically unsaturated carboxylic acids with the same number of carbon atoms as the hydrocarbon having serious shortcomings. The catalysts either have a very short active life, or they convert only a portion of the hydrocarbon to desired end groups per pass; they oxidize the hydrocarbon excessively to form high proportions of carbon monoxide or carbon dioxide or both; they are not sufliciently selective, so that the hydrocarbon molecule is attacked at both the olefinic unsaturation and at a methyl group; or the oxidation of the olefin does not proceed beyond the aldehyde stage.

It is therefore unexpected to find a catalyst having unusually long life that will convert a substantial amount, more than 50% per pass, of a gaseous monoolefin such as propylene or isobutylene to yield very high proportions of acrolein and acrylic acid or methacrolein and methacrylic acid. It is also unexpected to find a catalyst that produces a Wide range of ratios of olefinic aldehyde to monoolefinically unsaturated carboxylic acid by controllable changes in reaction conditions or catalyst composition. Mol percent efficiencies of about 8 to 60 for the aldehyde and about 16 to 45 for the unsaturated carboxylic acid have been obtained with the catalyst and process of this invention. Usually When the efficiency for conversion of the hydrocarbon to aldehyde is high the efficiency for the conversion to acid is low and vice versa. This provides a great degree of flexibility in the process, so as to provide means for obtaining a product mix that is needed at any particular time during commercial operation.

THE REACTANTS The essential reactants are (1) propylene or isobutylene and (2) an oxygen containing gas, which can be pure oxygen, oxygen diluted with an inert gas, oxygen enriched air or air without additional oxygen. For reasons of economy, air is the preferred oxygen containing reactant.

atent 0 For the purpose of this invention the hydrocarbons which are oxidized can be defined generically by the formula wherein it is also apparent that the end products formed result from the oxidation of only one methyl group on the hydrocarbon molecule While the terminal CH2=( J- remains intact.

Stoichiometric ratios of oxygen to olefin for the purpose of this invention are 1.5 to 1. Slightly lower amounts of oxygen can be used at a sacrifice of yield. It is preferred, however, to use 33 to 66% excess oxygen. Larger excesses do not impair the yields of aldehydes and acids, but for practical considerations an excess much above 'would require extremely large equipment for a given production capacity.

The addition of steam into the reactor along with the hydrocarbon and oxygen containing gas is desirable but not absolutely essential. The function of steam is not clear, but it seems to reduce the amount of carbon monoxide and dioxide in the eflluent gases.

Other diluent gases can be used. Surprisingly, saturated hydrocarbons such as propane are rather inert under the reaction conditions. Nitrogen or other known inert gases can be used as diluents if desired.

THE CATALYST AND ITS PREPARATION There are several methods for the preparation of the catalyst, which can be supported or unsupported. It is possible to dissolve each of the starting ingredients in water and combine them from the aqueous solutions or the ingredients can be dry blended. Because of the more uniform blend obtained by the solution procedure, it is preferred.

The general procedure for preparing a catalyst from water soluble ingredients is to dissolve the requisite amount of a molybdenum salt, a tellurium salt and the Group VIII metal salt in water. Add the requisite amount of phosphoric acid to the Group VIII metal salt so ution. Add the tellurium salt solution to the molybdenum salt solution and then add the Group VIII metal salt-phosphoric acid mixture to the molybdenum-tellurium salt mixture. The catalyst is then dried and baked at 400 C. for about 16 hours.

Supported catalysts can be prepared by adding a dry support or an aqueous slurry thereof to the aqueous solution of catalyst or the aqueous catalyst ingredients can be added to the slurry of the support.

Alternatively, a slurry of the catalyst ingredients can be prepared in water, then dried and baked. For supported catalysts the aqueous slurry of the catalyst ingredients can be added to an aqueous suspension of the support or vice versa, and then dried and baked.

Another method is to blend the dry ingredients of the desired particle size and then mix them thoroughly. Thorough blending and uniform particle size is desired.

A specific example of the solution method is now set forth.

In this procedure the ingredients are precipitated on blending.

(a) Dissolve 105.96 g. of ammonium molybdate (4H O) in ml. distilled Water at about 50 C.

(b) Di -solve 31.922 g. TeO in 80 ml. concentrated HCl and filter if necessary. Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(0) Dissolve 54.06 g. FeCl .6H O in water and add W 23.1 g. of 85% H PO Add this mixture slowly to the precipitated ammonium molybd-ate-TeO mixture.

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, the catalyst is ground to the desired mesh size and sieved. For supported catalysts an aqueous slurry of the support can be added to the catalyst ingredients, or vice versa, prior to drying and baking.

A supportedcatalyst may be prepared by adding to (c) 240 grams of an aqueous colloidal dispersion of microspheroidal silica in a concentration of 30-35% Si (Ludox H.S.). The silica may also be added to one of the individual ingredients or (c) to the silica dispersion.

Among the suitable supports are silica, silica containing materials, such as diatomaceous earth, kieselguhr, silicon carbide, clay, aluminum oxides and even carbon, although the latter tends to be consumed during the reaction.

The exact chemical structure of the catalysts made by the above procedures is not known, but catalysts with molar ratios of 100 Mo, l00 Te and l0-l00 of a Group VIII metal phosphate can be used for oxidizing the monoolefinic hydrocarbon to aldehyde and/or carboxylic acid. The catalyst contains chemically bound oxy gen so that the generic formula can be written as or other Group VIII metal phosphate 10-100. The phosphate can be a PO, radical, a pyrophosphate, or a polyphosph-ate, for example, ferrous phosphate, ferric phosphate, ferric pyrophosphate, nickel orthophosphate, nickel pyrophosphate, cobalt phosphate and the like.

Useful catalysts are ones having ratios of 100 M00 33.33 TeO and 66.66 co P O 100 M00 33.33 TeO and 66.66 NizPzOq; 100 M00 33.33 TeO and 33.33 FePO and 100 M00 33.33 TeO and 66.66 F4(P2O7)3 because they give high yields of desired products, and the preferred support is silica, because of its low cost and good fluidizing characteristics.

REACTION CONDITIONS The reaction can be carried out in either a fixed or fluidized catalyst bed.

The reaction temperature can range from about 300 to 525 C. for the oxidation of propylene but the preferred range is from about 350 to about 500 C. Below 350 C. the conversion per pass is lower and low temperature tends to produce more aldehyde than desired. Usually, a longer contact time is needed at lower temperatures to obtain the yields of desired products obtainable at higher temperatures. Above 500 C. in the propylene oxidation some of the desired end products appear to be oxidized to carbon oxides. For isobutylene, oxidation temperatures of 375-550 are desirable with the preferred range being 300-450 C.

The molar ratio of oxygen to propylene or isobutylene should be at least 2 to l for good conversion and yields. Some excess oxygen, 33 to 66 mol percent is even more desirable and is preferred. There is no critical upper limit as to the amount of oxygen, but when air is used as the oxygen containing gas it becomes apparent that too great an excess will require large reactors, pumping, compressing and other auxiliary equipment for any given amount of desired end product. It is therefore best to limit the amount of air to provide a 33 to 66% excess of oxygen. This range provides the largest proportion of acid, under given reaction conditions. Also, since care is needed to avoid an explosive mixture, the limiting of air aids in that direction.

The molar ratio of steam to propylene or isobutylenc can range from 0 to about 5 to 7, but best results are obtained with molar ratios of about 3 to 5 per mol of olefin and for this reason are preferred.

The contact time can vary considerably in the range of about 2 to seconds. Best results are obtained in a range of about 8 to 54 seconds and this range is preferred. Longer contact times usually favor the production of acid at any given temperature.

The particle size of catalyst for fixed bed operations used is from 10-18 mesh. As is known, for fixed beds, the size may be of a wider range particle size. For fluid bed systems the catalyst size should be from -325 mesh (US. Sieve).

The reaction can be run at atmospheric pressure, in a partial vacuum or under induced pressure up to 50100 p.s.i. Atmospheric pressure is preferred for fixed bed systems and a pressure of l to 100 psi. for fluid bed reactions. Opcration at a pressure which is below the dew point of the unsaturated acid at the reaction temperature is advantageous.

The data in the examples show that wide variations in percentages of unsaturated acids and aldehydes can be obtained with a single catalyst, using fixed ratio of reactants but changing the temperature and/or contact time. Further variation is obtainable by controlling the other variables in the reaction including the catalyst compositions Within the limits set forth herein.

The examples are intended to illustrate the invention but not to limit it.

THE EXAMPLES A series of runs was made in a fixed bed reactor of a high silica (Vycor) glass tube 12 inches long and 30 mm. outer diameter. The reactor had three inlets, one for air, one for steam and one for propylene. Three external electrically operated heating coils Were wound on the reactor. One of the coils extended along the entire length of the reactor and each of the remaining coils extended only about one-half the length of the reactor.

Outlet vapors were passed through a short water cooled condenser. Uncondensed gases were passed through a gas chromatograph (Perkin-Elmer Model 154D) and analyzed continuously. The liquid condensate was weighed and then analyzed for acrylic acid and acrolein in the gas chromatograph.

Example 1 The reactor was filled to about of its capacity with 170 ml. of catalyst made by the solution method described :above, with FeCl using a ratio of 75 M00 25 TeO and 25 FePO Empirically, the catalyst is Mo Te Fe P O and '[hC P iS present as P04. The catalyst was not supported and had a mesh size of 10- 18 (U5. Sieve).

Steam at a temperature of 200-25 0 C. was first passed into the reactor. Then propylene and air were separately fed into the stream of water vapor. This mixture then passed through a preheater and entered the reactor at about 200-250" C. The reactor was pre-heated to about 285 C. before the gas feed was begun. The ratio of reactants was about 2.955 mols of oxygen and 4.36 mols of steam per mol of propylene. Cold contact time is as set forth in the table below. The reaction temperature was 3 varied as the reaction proceded.

AA=Acrylic acid.

Example 2 For a second series a pyrophosphate catalyst was made as described, with 108 g. FeCl 6H O and 69.2 g. of phosphoric acid.

The reactor was filled to about 90% of its capacity with 170 ml. of this catalyst made by the solution method described above, using a ratio of 75 M00 25 Te0 and 12.5 Fe (P O Empirically the catalyst is and the P is present as IP O The catalyst was not supported and had a mesh size of -18 (U.S. Sieve).

Steam at a temperature of ZOO-250 C. was first passed into the reactor. Then propylene and air were separately fed into the stream of water vapor. This mixture then passed through a pre-heater and entered the reactor at about ZOO-250 C. The reactor was pre-heated to about 285 C. before the gas feed was begun. The ratio of reactants was about 2.955 mols of oxygen and 4.36 mols of steam per mol of propylene. Cold contact time was 45 seconds. The reaction temperature was varied as the re action proceeded.

The table below summarizes the data obtained in these runs:

A nickel catalyst was made as follows:

(a) Dissolve 105.96 g. of ammonium molybdate in 130 ml. distilled water.

(b) Dissolve 31.922 g. TeO in 80 ml. concentrated HCl and filter if necessary.

Add the tellurium salt solution to the ammonium molybdate solution. A precipitate forms.

(c) Dissolve 95.08 g. NiCl .6H O in 110 ml. of Water and add 46.2 g. of 85% H PO Add this mixture slowly to the precipitated amomnium molybdate-TeO mixture.

Dry on a steam bath and bake for 16 hours at 400 C. Thereafter, the catalyst is ground to the desired mesh size and sieved. For supported catalysts an aqueous slurry of the support can be added to the catalyst ingredients, or vice versa, prior to drying and baking.

The reactor was filled to about 90% of its capacity with 170 ml. of this catalyst made by the solution method described above, having a ratio of 75 M00 TeO and 25 Ni P O Empirically the catalyst is and the P is present as P O The catalyst was not supported and had a mesh size of l0'18 (U.S. Sieve). Steam at a temperature of ZOO-250 C. was first passed into the reactor. Then propylene and air were separately fed into the stream of water vapor. This mixture then passed through a pre-heater and entered the reactor at about 200-250 C. The reactor was pre-heated to about 285 C. before the gas feed was begun. The ratio of reactants was about 2.955 mols of oxygen and 4.36 mols of steam per mol of propylene. Cold contact time was 20 seconds. The reaction temperature was 410 C. Acrolein and acrylic acid were obtained as a mole percent efficiency of 40.41 and 30.82.

Example 4 A cobalt catalyst was made in the same manner as in Example 3 and with the same weight reactants, 95.2 g. CoCl -6H O. The reactor was filled to about 90% of its capacity with 170 ml. of this catalyst made by the solution method described above, using a ratio of 75 M00 25 TeO and 25 Co P O Empirically the catalyst is and the P is present as P 0 The catalyst was not supported and had a mesh size of 10-18 (U.S. Sieve). Steam at a temperature of 200-250 C. was first passed into the reactor. Then propylene and air were separately fed into the stream of water vapor. This mixture then passed through a pre-heater and entered the reactor at about 200250 C. The reactor was pre-heated to about 285 C. before the gas feed was begun. The ratio of reactants was about 2.955 mols of oxygen and 4.36 mols of steam per mol of propylene. Cold contact time was 45 seconds. The reaction temperature was varied as the reaction proceecled.

The table below summarizes the data obtained in these runs:

Mol percent elficiency Run No. Temp., C.

Aor. AA

Aer. =Acrolein.

AA=Acrylie acid.

I claim:

1. A method of preparing a mixture of unsubstituted monooletinic aldehydes and monoolefinic monocarboxylic acids by oxidation of a methyl group of a hydrocarbon having the structure comprising passing through a catalyst bed a mixture of gases having a molar ratio of 1 mol of said monoolefinic hydrocarbon, an oxygen containing gas containing about 1.5 to 4 mols of oxygen and up to 7 mols of water vapor per mol of said monoolefinic hydrocarbon, at a temperature of from about 325 C. to about 500 C., the said catalyst consisting essentially, on a molar basis, of

wherein M is a Group VIII metal of the fourth period of the periodic table, and in which each P atom is combined with 3 to 4 atoms of oxygen and the M to P ratio ranges from IM to 1P to 4M to 61, at a temperature of from about 350 C. to about 450 C.

3. The method of claim 2 in which the M to P ratio is l.

4. The method of claim 2 in which the catalyst has th empirical formula Mo Te C0 P O and the P is present as pyrophosphate.

5. The method of claim 2 in which the catalyst has the empirical formula Mo Te Ni P O and the P is present as pyrophosphate.

6. The method of claim 2 in which the catalyst has the empirical formula 100 33.3 33.(i-26.6 33.3-100 500716 and the P is present as pyrophosphate and phosphate.

7. The method of claim 2 wherein the catalyst contains, in molar ratios, 100 M00 10400 Te0 and 10-100 CO2P2O7.

8. The method of claim 2 wherein the catalyst contains, in molar ratios, 100 M00 10-100 TeO and 10-100 N12P2OI1.

9. The method of claim 2 wherein the catalyst contains, in molar ratios, 100 M00 10-100 TeO and 10-100 FCPO4.

10. The method of claim 2 wherein the catalyst contains, in molar ratios, 100 M00 10-100 TeO and 10- 100 Fe P O 11. A method of preparing a mixture of acrylic acid comprising passing a mixture of propylene, an oxygen containing gas containing from about 1.5 mols of oxygen per mol of propylene and up to 7 mols of water vapor per mol of propylene through a bed of a catalyst comp g 1no as.a ss.a ss.s as.s 100 5ou-'716 wherein M is a Group VIII metal of the fourth period of the periodic table, and in which the P is present as P 0 at a temperature of from about 360 to about 425 C.

12. A method of preparing a mixture of methacrolein and methacrylic acid comprising passing a mixture of iso- 20 butylene and an oxygen containing gas in an amount sufficient to provide from about 1.5 mols to about 3 mols of oxygen per mol of isobutylene, through a bed of a catalyst c0mprising MOmT1 1 M2 2gP2 20O 9 120 Wherein M is a Group VIII metal of the fourth period of the periodic table, and in which the M to P ratio ranges from M to P to M to P and in which each P is combined with 3 to 4 atoms of oxygen.

References Cited UNITED STATES PATENTS 3,065,264 11/1962 Koch et al. 260533 3,098,102 7/1963 Bethell et a1 260604 3,192,259 6/1965 Fetterly et a1. 260533 FOREIGN PATENTS 903,034 8/ 1962 Great Britain.

OTHER REFERENCES Derwent delayed Belgian Report, No. 28, Aug. 21, 1964; General Organic sec., p. 1. 260533.

HENRY R. JILES, Primary Examiner.

D. E. STENZEL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,401,197 September 10, 1968 Jamal S. Eden It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, lines 24 and 25, the formula should appear as shown below:

lO l10 2-2O 220 39-120 Column 5, line 9, the formula 'should'appear as shown below:

same column 5, in the table, heading'tothesecond column, line 3 thereof,

' "propitylene" should read propylene converted Same bl second column line 1 thereof, "260" should read 360 Signed and sea1ed-this lfith'day' of March 1970.

(SEAL) Attest "EDWARD"MIFLETCHER,JR. WIIILIAME*-"SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

1. A METHOD OF PREPARING A MIXTURE OF UNSUBSTITUTED MONOOLEFINIC ALDEHYDES AND MONOOLEFINIC MONOCARBOXYLIC ACIDS BY OXIDATION OF A METHYL GROUP OF A HYDROCARBON HAVING THE STRUCTURE 